The question of what is excessive current flow; It can be answered as a current system used to prevent any damage to the electric motor running over current.
Electrical fuses are placed at the beginning of the circuits and thus ensure the protection of the line. Likewise, various circuits of current are used to protect this electric fuse motor.
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What is the Structure of the Overcurrent Relay?
The overcurrent supply shows the conductor according to the phase transitions that the electric current circuit has. It is a 3-phase electric current circuit, that is, in a structure that is connected to 3 conductors.
Over Current Relay
I. Thermal Characteristic Overcurrent Relay
II. Directional Overcurrent Relay
III. Dependent Overcurrent Protection Relay
This current protection state is generally used for motor and mains protections. For example, it is preferred to protect short-term but pulsed motor systems. That is, during the selective protection period, there are structures related to short-circuit operation.
IV. Independent Overprotection Relay
The selective protection time period does not occur simultaneously with the current setting. Independent current protection current is preferred for motor, mains, or generator protection.
Distance Protection Relay
The distance between the relay and the fault location can also be measured by impedance. According to the distance length defined in the relay, the relay uses the appropriate breaker or uses the supporting task.
Differential Relay
When the secondary terminals on the current transformers are connected reversely, 180 degrees phase difference occurs and it is added to the current relay. This current relay is defined as a differential relay. In addition, these types of relays are known as relays that detect short circuits caused by insulation failure without any problems.
How is the Overcurrent Relay Operating System?
If there is a current value at a normal value, the output contacts are pulled. If this current is found to be higher than the desired value, the output contacts open with a delay and also disable the system it is connected to.
The current relay system is connected in series on the motor circuit and the required current from the network passes through the current relay. At first, the overload passing through the circuit does not cause any damage, but if this situation continues continuously, it may cause damage to the motor. The engine heats up to an undesirable degree and may catch fire.
If there is excess current on the motor circuit for any reason, this excess current also passes through the relay. In this way, the overcurrent switch is actually turned on and the energy load is somehow stopped and cut off. In the end, the motor is disabled and the circuit structure is preserved without any damage.
In addition, the current relay, which is closed due to overcurrent, can be made usable again with the reset button.
What are the Types of Overcurrent Relays Used in the Electrical System?
Current relays are divided into two categories according to their structures:
Thermal Overcurrent Relay
The motor current can generate a high temperature and radiate heat while it is running. The current relay that works overtime with this temperature effect is called the thermal current relay and is divided into three types.
I. Melting Alloy Thermal Overcurrent Relay
The fusing alloy thermal current relay is made up of a contact block and a small heater tube. The tube is located around the heater source and there is another free standing second tube. Between these two separate tubes is an alloy that melts when it comes into contact with heat. This molten alloy acts as a bridge between two tubes.
II. Thermal Overcurrent Relay with Indirect Heating
Indirectly heated thermal overcurrent relay consists of a heater, contact, and bi-metal components. An indirectly heated relay is connected in series to the motor circuit providing the heater effect. The motor current is transferred over the heater, but if this current is at a level that will damage the motor, the metal becomes curved to the right. In this way, the engine is protected from burning quickly and safely.
If the motor current is above the required values, even for a short time, the bi-metal on the motor will not have time to warm up. In this way, the overcurrent relay is stopped.
However, for large and high currents, these indirectly heated relays are not preferred as they will make the current severe.
III. Direct Heating Thermal Overcurrent Relay
Relays without a heater element are called direct-heated thermal relays. The required motor current passes through the bi-metal. Again, it is not very suitable and useful for large and high currents.
Magnetic Overcurrent Relay
The metal, which is in a created magnetic field, is called magnetic charge, current in its direction. That is, the motor current operates in a magnetic field. Magnetic current fluctuation consists of parts such as an electromagnet, a retarder element, and contact.
D- How Should the Excess Scheme Used in the Electrical System Be?
Overcurrent relays used in the electrical system are connected in series on the motor circuit. Motor current flows through this circuit. Thanks to the short-time currents provided by the motor, no damage occurs in the circuit. Thus, a delaying system prevents the relay from keeping the circuit open.
E- Overcurrent Relay Installation Used in Electrical Systems
An overcurrent relay can be mounted on a rail or surface. With the help of a cutter drill, the determined place is drilled and the remaining assemblies are corrected with a screwdriver. Various contact structures, contact brands, and sizes are also available and used to maintain the electrical system layout.
Published On - 7 December 2022